Author/Authors :
Belli، نويسنده , , P. and Cerulli، نويسنده , , R. and Danevich، نويسنده , , F.A. and Grinyov، نويسنده , , B.V. and Incicchitti، نويسنده , , A. and Kobychev، نويسنده , , V.V. and Laubenstein، نويسنده , , M. and Nagorny، نويسنده , , S.S. and Tolmachev، نويسنده , , A.V. and Tretyak، نويسنده , , V.I. and Yavetskiy، نويسنده , , R.P.، نويسنده ,
Abstract :
A small Li 6 Eu ( BO 3 ) 3 crystal (2.72 g) was measured deep underground at the Gran Sasso National Laboratories with a HP Ge detector of 408 cm 3 during 1500 h. While the crystal is not polluted by usual radioactive contaminants (only limits on the activity of U/Th chains, 40K, 60Co, 137Cs were set on the level of 0.01–1 Bq/kg), the presence of radioactive 152Eu and 154Eu is evident; these are created in capture of neutrons by naturally abundant 151Eu and 153Eu. The measured activities correspond to 0.95 and 0.21 Bq/kg for 152Eu and 154Eu, respectively, with a ratio far from the standard expectation. As by-products, limits on half lives for the α decays Eu 151 → Pm 147 ( E exc = 91.1 keV ) and Eu 153 → Pm 149 are determined as T 1 / 2 > 2.4 × 10 16 yr and T 1 / 2 > 1.1 × 10 16 yr , respectively.
Keywords :
Li 6 Eu ( BO 3 ) 3 crystal , alpha decay , 152Eu , 151Eu , 153Eu , 154Eu , Neutron capture
